Primary neuroendocrine carcinoma of the vagina with Merkel cell carcinoma phenotype.

We describe a case of primary neuroendocrine carcinoma arising from the anterior vaginal wall of a 67-year-old woman. Primary neuroendocrine carcinoma of the vagina is a rare entity with only 25 previously reported cases in the literature. In previous reports, these tumors have not been distinguished from primary neuroendocrine carcinoma of the skin (Merkel cell carcinoma). The tumor was composed of cells that showed neuroendocrine-type nuclear features with hyperchromasia, nuclear molding, occasional small nucleoli, and a chromatin pattern that was finely granular. The tumor cells were positive for cytokeratin 20 (CK20), neuron specific enolase, pancytokeratin, epithelial membrane antigen, and chromogranin A expression. Ki-67, a marker of proliferation, was also positive in>90% of cells. The tumor cells showed intense expression of Bcl-2 oncoprotein and mild to moderate expression of c-KIT. Synaptophysin, neurofilament, CD45, CD56, CD10, S-100, HMB-45, cytokeratin 7, and thyroid transcription factor 1 were negative. This pattern of staining is consistent with a Merkel cell carcinoma. This is the first report of a primary neuroendocrine carcinoma of the vagina with a Merkel cell phenotype. Previous studies have not distinguished primary neuroendocrine carcinoma of the vagina from Merkel cell carcinoma of the skin. Positive expression of CK20 in primary small cell carcinoma of the vagina might represent a Merkel cell carcinoma subtype of this tumor.